# US 9,438,992 B2 · Multi-microphone robust noise suppression > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 9,438,992 B2 - Document ID: US9438992B2 - Status: Granted - Kind: B2 - Application number: 13/959,457 - Filed: 2013-08-05 - Published: 2013-12-05 - Granted: 2016-09-06 - Earliest claimed: 2010-04-29 - Assignees: Knowles Electronics, LLC - Applicants: Knowles Electronics, LLC - Inventors: Mark Every; Carlos Avendano; Ludger Solbach; Ye Jiang; Carlo Murgia - Web page: https://patentgrep.com/patent/US9438992B2 ## CPC - H04R 3/002: {Damping circuit arrangements for transducers, e.g. motional feedback circuits} - G10L 21/0208: Noise filtering - G10L 21/0232: Processing in the frequency domain - G10L 2021/02082: {the noise being echo, reverberation of the speech} - G10L 2021/02166: {Microphone arrays; Beamforming} - H04R: LOUDSPEAKERS, MICROPHONES, GRAMOPHONE PICK-UPS OR LIKE ACOUSTIC ELECTROMECHANICAL TRANSDUCERS; ELECTRIC HEARING AIDS; PUBLIC ADDRESS SYSTEMS (producing sounds with frequency not determined by supply frequency G10K) - G10L: SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING ## Abstract A robust noise reduction system may concurrently reduce noise and echo components in an acoustic signal while limiting the level of speech distortion. The system may receive acoustic signals from two or more microphones in a close-talk, hand-held or other configuration. The received acoustic signals are transformed to frequency domain sub-band signals and echo and noise components may be subtracted from the sub-band signals. Features in the acoustic sub-band signals are identified and used to generate a multiplicative mask. The multiplicative mask is applied to the noise subtracted sub-band signals and the sub-band signals are reconstructed in the time domain. ## Claims ### Claim 1 A system for performing noise reduction in an audio signal, the system comprising: a memory; a frequency analysis module stored in the memory and executed by a processor to generate a plurality of sub-band signals in a frequency domain from time domain acoustic signals; a noise cancellation module stored in the memory and executed by a processor to cancel noise in one or more of the plurality of sub-band signals; a modifier module stored in the memory and executed by a processor to suppress a noise component and an echo component in the one or more noise canceled sub-band signals on a per sub-band basis; and a reconstructor module stored in the memory and executed by a processor to reconstruct a modified time domain signal from the components suppressed sub-band signals provided by the modifier module. ### Claim 2 (depends on 1) The system of claim 1, wherein the time domain acoustic signals are received from one or more microphone signals on an audio device. ### Claim 3 (depends on 1) The system of claim 1 further comprising a feature extraction module stored in memory and executed by a processor to determine features of the sub-band signals, the features determined for each frame in a series of frames for the acoustic signals. ### Claim 4 (depends on 3) The system of claim 3, the feature extraction module configured to control adaptation of the noise cancellation module or the modifier module based on inter-microphone level difference or inter-microphone time or phase differences between a primary acoustic signal and a second, third or other acoustic signal. ### Claim 5 (depends on 1) The system of claim 1, the noise cancellation module cancelling at least a portion of the plurality of sub-band signals by subtracting the noise component or by subtracting the echo component from the one or more of the plurality of sub-band signals. ### Claim 6 (depends on 5) The system of claim 5, further comprising: a feature extraction module stored in memory and executed by a processor to receive the plurality of sub-band signals from the frequency analysis module, and determine features of each of the plurality of the sub-band signals, the features determined for each frame in a series of frames for the acoustic signals, wherein a determined feature is a null-processing inter-microphone level difference derived in the feature extraction module from output of the one or more noise canceled sub-band signals from the noise cancellation module and from the plurality of received sub-band signals. ### Claim 7 (depends on 1) The system of claim 1, further comprising a mask generator module stored in memory and executed by the processor to generate a mask, the mask configured to be applied by the modifier module to sub-band signals output by the noise cancellation module. ### Claim 8 (depends on 7) The system of claim 7, further comprising: a feature extraction module stored in memory and executed by a processor to determine features of the sub-band signals, the features determined for each frame in a series of frames for the acoustic signals, wherein the mask is determined based partly upon one or more features derived in the feature extraction module. ### Claim 9 (depends on 8) The system of claim 8, wherein the mask is determined based at least in part on a threshold level of speech-loss distortion, a desired level of noise or echo suppression, or an estimated signal to noise ratio in each sub-band of the sub-band signals. ### Claim 10 A method for performing noise reduction in an audio signal, the method comprising: executing a stored frequency analysis module by a processor to generate sub-band signals in a frequency domain from time domain acoustic signals; executing a noise cancellation module by a processor to cancel at least a portion of the sub-band signals; executing a modifier module by a processor to suppress a noise component and an echo component in the noise canceled portion of the sub-band signals on a per sub-band basis; and executing a reconstructor module by a processor to reconstruct a modified time domain signal from the components suppressed sub-band signals provided by the modifier module. ### Claim 11 (depends on 10) The method of claim 10, further comprising receiving time domain acoustic signals from one or more microphone signals on an audio device. ### Claim 12 (depends on 10) The method of claim 10, further comprising determining features of the sub-band signals, the features determined for each frame in a series of frames for the acoustic signals. ### Claim 13 (depends on 12) The method of claim 12, further comprising controlling adaptation of the noise cancellation module or the modifier module based on inter-microphone level difference or inter-microphone time or phase differences between a primary acoustic signal and a second, third or other acoustic signal. ### Claim 14 (depends on 10) The method of claim 10, further comprising: determining features of the sub-band signals, the features determined for each frame in a series of frames for the acoustic signals, wherein a feature is derived in a feature extraction module from output of the noise cancellation module and from the canceled portion of the sub-band signals. ### Claim 15 (depends on 10) The method of claim 10, further comprising generating a mask, the mask configured to be applied by the modifier module to sub-band signals output by the noise cancellation module. ### Claim 16 (depends on 15) The method of claim 15, further comprising: determining features of the sub-band signals, the features determined for each frame in a series of frames for the acoustic signals, wherein the mask is determined based partly upon one or more features derived in a feature extraction module. ### Claim 17 (depends on 16) The method of claim 16, wherein the mask is determined based at least in part on a threshold level of speech-loss distortion, a desired level of noise or echo suppression, or an estimated signal to noise ratio in each sub-band of the sub-band signals. ### Claim 18 A non-transitory computer readable storage medium having embodied thereon a program, the program being executable by a processor to perform a method for reducing noise in an audio signal, the method comprising: executing a stored frequency analysis module by a processor to generate a plurality of sub-band signals in a frequency domain from time domain acoustic signals; executing a noise cancellation module by a processor to cancel noise in one or more of the plurality of sub-band signals; executing a modifier module by a processor to suppress a noise component and an echo component in the one or more noise canceled sub-band signals on a per sub-band basis; and executing a reconstructor module by a processor to reconstruct a modified time domain signal from the components suppressed sub-band signals provided by the modifier module.